Vertical shaft impact crushers (VSI-crushers) are used in many applications for crushing hard material, such as rocks, ore, etc. U.S. Pat. No. 4,690,341 describes one example of such a VSI-crusher. A VSI-crusher comprises a housing and a horizontal rotor located inside the housing. Material that is to be crushed is fed into the rotor via an opening in the top thereof. With the aid of centrifugal force, the rotating rotor ejects the material against the wall of the housing. On impact with the wall of the housing, the material is crushed to a desired size. The housing wall could be provided with anvils or have a bed of retained material against which the accelerated material is crushed.
The rotor of a VSI-crusher usually has a horizontal upper disc and a horizontal lower disc. The upper and lower discs are connected with a vertical rotor wall. The upper disc has an aperture for feeding material into the rotor. The material lands on the lower disc and is then thrown out of the rotor via openings in the rotor wall. A replaceable center distributor plate is mounted on the horizontal lower disc to protect the same from the material fed to the rotor. The horizontal lower disc of U.S. Pat. No. 4,690,341 is protected by a replaceable circular center distributor plate. WO 2004/020101 illustrates a replaceable hexagonal center distributor plate, which has been found to provide a longer life than the circular ones.
When the center distributor plate has been worn out, it must be replaced, a task which includes a complicated maintenance procedure.